Fix grammar

wiki/src/doc/encryption_and_privacy/secure_deletion.mdwn

@@ -139,7 +139,7 @@ be deleted during the operation.
   1. Click on the disk that you want to clean in the left pane to
      navigate to the root of this disk.
 
-  1. Right-click in empty space in the right pane and choose <span
+  1. Right-click in the empty space in the right pane and choose <span
      class="guimenuitem">Wipe available diskspace</span>.
 
      [[!img wipe_available_diskspace.png link=no alt="Right-click&nbsp;▸ Wipe